This invention relates generally to a container for a fluid to be tested under pressure and more particularly, but not by way of limitation, to a positive sealed slurry cup for a consistometer.
In the oil and gas industry, different fluids are used for various purposes in drilling and completing a well. For example, batches of cement slurry must be mixed and pumped into the well for cementing casing into the well bore. The cement is generally pumped through the casing and up the annulus between the casing and the well bore to create the necessary bond.
Because different batches of fluids (e.g., cement slurries) can have different characteristics which affect how the fluids perform in the high temperature and high pressure environments found downhole, there is the need for equipment which can test a fluid sample prior to the fluid being pumped downhole so that one can determine if that particular batch of fluid has the proper characteristics for the particular situation. Such a type of equipment, known as a consistometer or viscometer, is known to the art.
To pressurize the fluid under test in a consistometer of a type known to the art, a pressurized fluid is applied to one side of a sealed boundary separating the pressurized fluid from the test fluid. Not only must a seal be provided at this boundary, but also a sealed passageway through the seal must be provided to receive a paddle shaft or a tube in which a thermocouple is housed for monitoring the temperature of the test fluid. Heretofore, this passageway has been provided through one or more diaphragms or plates sealing directly around the shaft or tube. These diaphragms or plates extend across the annulus between the outside of the tube or shaft and the inside of the cup in which the test fluid is held. A diaphragm and bushing construction wherein O-rings carried by the bushing seal against the tube or shaft has also been used.
A shortcoming of these types of constructions is that when enough air bubbles are contained within the test fluid, the diaphragms or seal rings or plates of these prior constructions tend to collapse or deform toward the test fluid when the pressurized fluid is applied. This collapsing or deforming can break the seal formed at the edge where the seal member is to engage the tube or shaft extending therethrough, thus allowing the pressurized fluid to leak into the chamber where the test fluid is. The pressurized fluid, such as mineral oil, can contaminate the test fluid or can create a thin film on the inner surface of the cup containing the test fluid. This contamination or film can adversely affect the accuracy of the pumping time or viscosity analyses which were intended to be made.
Another noted shortcoming of these constructions which attempt to seal around a rotatable shaft is that excess friction may result when the shaft is rotated, such as in response to increasing viscosity of the test fluid, for example.
Therefore, there is the need for a new container for a fluid to be tested under pressure wherein the test fluid is more positively isolated from the pressure medium while still being able to rotate or detect the rotation of a paddle through the test fluid and while also still being able to receive a thermocouple for monitoring the temperature of the test fluid. Such a container should be specifically useful for high pressure, high temperature cement slurry testing consistometers.